Foundry mold composition



United States Patent Arthur G. Clem, Des Plaines, Ill., assigner to American Colloid Company, Skokie, 111., a corporation of Delaware No Drawing. Filed July 9, 1 957, Ser. No. 670,650 4 Claims. (Cl. 260-25) This application relates to green sand mold compositions and the production thereof. More particularly, it relates to foundry mold compositions comprised of sand, bentonite or similar clay bonding mineral, a resinous organic binder and an aqueous solution of a lower watermiscible organic solvent, and to methods for the production of such compositions.

In the foundry industry cores composed of sand and binding agents are placed in sand molds to create cavities or voids in castings. Such cores should have good Wet strength so that they retain their configuration and size when formed from moist materials. These cores should also be fairly hard when baked and should have good surface hardness, that is, the sharp edges and configurations should be rigidly hard and not break off or wash away when subjected to a stream of molten metal. After the casting has been poured and the metal has set the core composition should have relatively low retained strength so that the core can be readily broken up and poured out of the casting. On the other hand, the core composition should have good hot strength so that it retains its shape and configuration when subjected to hot molten metal. Cores with good hot strength form sharp precision castings which are required for many types of foundry practice.

In the past, core compositions have been produced by mixing sand with an unsaturated oil, such as linseed oil or tall oil, and with cereal binders prepared from corn starch and dextrin. Such oil-bonded core compositions are relatively weak when wet but are cohesive and can be baked to a material having relatively good baked strength due to the polymerization of the unsaturated oils to form polymers which bond the particles of sand together. Such baked cores are very hard and are almost ceramic in nature. However, such core compositions do not withstand molten metal satisfactorily because they have very poor hot strength. Parts of the oil-bonded cores are washed away by the molten metal during casting, causing metal penetration. Castings thus produced are often distorted in size or shape, are not uniform and often contain sand which is washed away from the core material. In addition, the oils of oil-bonded cores create gases at casting temperatures and the gases may boil back into the molten metal, leaving fissures in the casting which are objectionable.

To increase the hot strength of core compositions, swelling clays which resist high temperature have been added thereto. For instance, core compositions composed of sand, bentonite, linseed oil and organic binders have relatively good hot strength but the baked strength of the core is reduced and the retained strength is increased. Therefore, after the core has been formed and baked it is subject to Weakness at sharp edges and configurations with the result that parts of the core are worn or broken away in handling, leading to castings having configurations other than that desired. To overcome the low baked strength of .oil bonded green sand cores, other materials have been substituted for oils, such as rosin or liquid phenolic resin binders. Despite the addition of organic resin and rosin binders to green sand cores containing bentonite, the surface hardness properties of cores from such compositions have not been as great as desired for precision foundry practice, and the retained strength of these cores ice has been too great for ready removal from castings.- There is a definite need for mold compositions having adequate wet strength, good baked strength, good surface hardness, relatively high hot strength, but low retained strength so that the cores may be readily removed from the castings. It is the purpose of this invention to provide new compositions which are suitable as green sand cores and which have the desirable properties listed above.

It is a further object of this invention to provide sand core compositions having adequate wet strength for ready formation, good baked strength for ease of handling and shipping or moving, good surface hardness so that sharp edges and minor configurations are rigidly hard to produce precision castings and good hot strength to resist erosion or disfiguration by molten metal, with relatively low retained strength so that the cores may be removed from the castings readily. It is also an object of this invention to provide methods of compounding green sand core compositions which satisfy the foregoing requirements. These and other objects Will be apparent from the following disclosure and are achieved in accordance with the invention as described below.

Broadly, the present invention concerns molding compositions comprising sand, bentonite or similar swelling mineral, a resinous organic binder and an aqueous solution of a lower organic water-soluble solvent. The resinous organic binder is preferably a combination of high softening point organic distillation residuum, such as a pitch, and a water-soluble phenolic resin, although either organic material may be used alone. The addition of the organic water-miscible solvent to the aqueous menstruurn used in producing the core compositions reduces the amount of water necessary for formulation, thereby controlling hydration of the swelling clay by depriving the clay of its total absorbable water and making the mixture easily handled. The organic solvent also aids in dissolving the resin binder and forming a sticky surface on each said grain which gives the core composition the desired surface hardness without the need for baking. Such cores have scratch-free surfaces and sharp edges. Cores formed from compositions of the type to which this invention pertains, exhibit added surface and hot strengths which are greatly desired in the foundry industry. For example, the hot strength of core compositions made in accordance with my invention, measured at 1650 F., are in excess of 600 lbs. per square inch and generally are in the range of 650 to 750 lbs. Similar compositions produced without the use of the water-miscible organic solvent in the formulation have hot strength considerably lower than that of this invention and generally in the order of 300 to 400 lbs. per square inch.

In producing green sand core compositions in accordance with this invention, there are four essential components. The first component is sand, preferably washed silica sand of foundry grade. The second constituent is a swelling mineral or clay, including bentonite, illite and high refractory kaolin, such as fire clay. The third constituent is a resinous organic binder, which may be made of two components, one being a high-melting pitch residue such as that from the distillation of tar or naval stores, and the other being a water-soluble or water-dispersible phenolic resin. Other pitch materials which can be used are gilsonite, pine pitch, rosin, powdered asphalt, coal tar pitch and petroleum pitch all of which are relatively highmelting resinous organic residuum materials having melting points in the range of 250 to 350 -F. and forming soft sticky masses at such temperatures. These pitch materials are at least partly soluble in alcohols and other water-miscible organic solvents and in aqueous solutions of such solvents. A second component of the resinous s k organic binder may be a liquid phenolic resin which is water-soluble or water-dispersible. Included are phenolformaldehyde resins, urea-formaldehyde resins and amineformaldehyde resins, such as melamine formaldehyde resins. These substances are water-compatible and thermosetting plastic materials. These materials are supplied in the form of water solutions or suspensions containing 50% to 80% solids and the solutions are generally slightly alkaline so that they are compatible with the swelling clays discussed above. It will be understood that the relative amounts of solid rosin and liquid resin which combine to form the organic binder may be varied over relatively wide ranges without departing from this invention.

The fourth component of the core compositions is an aqueous menstruum containing 25% to 75% of an organic water-miscible solvent such as methanol, ethanol, denatured alcohol, isopropanol, acetone, methyl ethyl ketone, dioxane and related volatile organic solvents which are miscible in water in proportions of 25 to 75 The organic solvents preferably have boiling points not greater than about 325 P. so that they may be evaporated at low temperature. The aqueous menstruum containing the organic solvent wets the swelling clay and dissolves the organic binders. The organic solvent deprives the swelling clay of the total amount of absorbable water, thereby permitting the mixture to be handled readily. In addition, the clay does not swell in the organic solvent and thereby dom not produce a core having high retained strength. Consequently, the core composition is readily broken away from the casting and avoids the disadvantageous high retained strength often exhibited by oilbonded sand cores.

The relative amounts of materials used in preparing green sand cores in accordance with this invention are generally as follows: For each 100 lbs. of clean sand there are added 2.5 to 6 lbs. of swelling clay and 0.5 to 3 lbs. of organic binder (preferably 0.5 to 1.5 lbs. of pitch binder combined with 0.25 to 1.5 lbs. (dry basis) of liquid phenolic resin binder). To the foregoing mixture is added a quantity of water-miscible organic solvent mixed with water in the concentration of 25% to 75%. The quantity of aqueous solution of water-miscible organic solvent is equal to about 75% to 150% the total weight of binder (clay plus organic binders). The combination of swelling clay and resinous organic binder is preferably made in a dry ingredient mixer for uniform distribution. The resin can be of the phenol-aldehyde, urea-aldehyde or amine-aldehyde type depending upon the hardness and grain-to-grain strength desired in the finished product.

Cores of this nature need not be baked to develop strength. They can be set on a rack to air dry or to evaporate moisture. They can be surface dried with an open flame of a torch until they are hard. They can be put into an oven at low temperature to evaporate the surface moisture only. By any of these methods the cores are ready for use within a short time.

The invention is disclosed by the following examples which are provided solely for purposes of illustration and are not to be interpreted as limiting the invention in scope. It will be appreciated by those skilled in the art that nuerous modifications in relative amounts of materials, temperatures, times and equivalent substances may be made without parting from the invention.

Example 1 About 4 lbs. of high-swelling, sodium base bentonite, either in powder or fine granular form, are intimately blended with /2 lb. (dry weight basis) of liquid ureaformaldehyde resin binder (Foundrez 7600 of Reichold Chemicals, Inc., which is a water-soluble thermosetting resin in water solution of density of lbs. per gallon). The mixing is done in a dry-ingredient mixer until uniform distribution is obtained. Then 2 lbs. of high-melting rosin (Vinsol of Hercules Powder Company) are thoroughly blended into the mixture to form a dry or faintly moist crumbly powder. This powder is added to 100 lbs. of washed silica sand and then 5% lbs. of 50% aqueous methanol are added. The mixture is thoroughly blended in a dry-ingredient mixer to form a green sand core composition.

Cores prepared from the above composition are placed on a rack to allow moisture to evaporate and air dry. The cores have good surface hardness and are satisfactory for gray iron, cast iron and steel alloy castings. The hot strength of the cores, measured at 1650 F., is in excess of 600 lbs.

Example 2 About 6 lbs. of high-swelling sodium bentonite are thoroughly mixed with 1.5 lbs. (dry weight basis) of liquid amine-formaldehyde resin binder (Foundrez 7605 of Reichold Chemicals, Inc., which is a water-soluble thermosetting resin in water solution of density about 9.7 lbs. per gallon) in a dry mixer. Then 1.5 lbs. of powdered asphalt are blended in. The mixture is added to 100 lbs. of washed sand, 7.5 lbs. of a 65% solution of denatured alcohol (S.D.A. 2A) in water are added, and the mixture is homogenized in a mixer. The core compositions thus produced does not pack on standing, has sutficient strength to be handled easily, and has general all-around good molding characteristics.

Cores prepared from the above composition by ramming into a standard body can be surface dried with the open flame of a torch until they are hard (10-15 minutes). The strength of such cores at high temperature is enhanced, due to movement of the liquid binder to the surface by reason of the rapid evaporation rate. The cores tested in excess of 700 lbs. hot strength at 1650 F.

Example 3 Five lbs. of illite and 1 /2 lbs. of gilsonite are ground together to form a uniform mixture. Then 100 lbs. of clean silica sand are added, followed by A lb. of phenolic resin binder (Foundrez 7500 of Reichold Chemicals, Inc., which is a powdered thermosetting phenol-formaldehyde resin). The mixture is mulled in a dry ingredient mixer with 7 lbs. of a 50% solution of acetone in water until homogeneous. The molding composition gives good cores with good surface hardness on air drying, without the need for baking. The cores may be baked at 250 350 F. for 30 minutes and may be used as they come from the oven; the hot strength of these cores is in the range of 650-700 lbs.-

Example 4 About 3 lbs. of bentonite and 1 lb. of high-melting rosin (Vinsol of Hercules Powder Company, a gasolineinsoluble residue from distillation of naval stores, melting in the range of 250-350 F.) are mulled together to a uniform mixture. Then the mixture is blended into 100 lbs. of washed sand with 5 lbs. of 30% aqueous isopropanol to form a moist powder. Cores are formed from the powder and baked at 350-450 F. for 12 minutes to evaporate surface moisture. Such cores have excellent surface hardness and are highly satisfactory in making gray iron and cast iron castings.

Example 5 About 4 lbs. of bentonite and 1 /2 lbs. (dry weight basis) of urea-formaldehyde resin (Foundrez 7600 of Reichold Chemicals, Inc.) are mixed in a mulling machine. The resulting mixture is blended into 100 lbs. of washed sand with 6% lbs. of aqueous methanol to form a moist powder. Cores formed from this powder exhibit good surface hardness on air drying and good hot strength at 1650 F.

of sand; 2.5 to 6 parts of a swelling clay selected from the group consisting of bentonite, illite and high refractory kaolin; 0.5 to 1.5 parts of a resinous organic binder selected from the group consisting of wood pitch, gilsonite, rosin, asphalt, coal tar pitch and petroleum pitch, having a melting point in the range of 250 to 350 F., combined with 0.25 to 1.5 parts (dry weight) of a synthetic resin selected from the group consisting of phenol-formaldehyde, urea-formaldehyde and melamine-formaldehyde resins, said resin being in the form of an aqueous dispersion containing 50% to 80% solids by weight; and an aqueous mentruum consisting of 25% to 75% water by weight and the remainder being a water-miscible organic solvent having a boiling point in the range of 108 to 325 F., the quantity of said aqueous menstruum being 75 to 150% of the total Weight of the swelling clay, resinous organic binder and synthetic resin.

2. A foundry mold composition as defined by claim 1 wherein the swelling clay is bentonite, the resinous organic binder is rosin, the synthetic resin is urea-formaldehyde resin and the water-miscible organic solvent is methanol.

3. A foundry mold composition as defined by claim 1 wherein the swelling clay is bentonite, the resinous organic binder is asphalt, the synthetic resin is melamineformaldehyde resin, and the water-miscible organic solvent is ethanol.

4. A foundry mold composition as defined by claim 1 wherein the swelling clay is illite, the resinous organic binder is gilsonite, the synthetic resin is phenol-formaldehyde resin and the water-miscible organic solvent is acetone.

References Cited in the file of this patent UNITED STATES PATENTS 2,270,770 Ray Jan. 20, 1942 2,313,672 Salzbery et a1. Mar. 9, 1943 2,378,366 Swain et a1. June 12, 1945 2,381,868 Abrams Aug. 14, 1945 2,407,225 Dixon Sept. 10, 1946 2,448,624 Rummelsburg Sept. 7, 1948 2,487,207 Adams Nov. 8, 1949 2,510,220 Grube June 6, 1950 2,525,175 Keyser Oct. 10, 1950 2,558,402 Wallace June 26, 1951 2,657,113 Barlow Oct. 27, 1953 2,662,067 Less et a1. Dec. 8, 1953 2,686,728 Wallace Aug. 17, 1954 2,830,342 Meyers et a1 Apr. 15, 1958 

1. A FOUNDRY MOLD COMPOSITION COMPRISING 100 PARTS OF SAND, 2.5 TO 6 PARTS OF A SWELLING CLAY SELECTED FROM THE GROUP CONSISTING OF BENTONITE, ILLITE AND HIGH REFRACTORY KAOLIN, 0.5 TO 1.5 PARTS OF A RESINOUS ORGANIC BINDER SELECTED FROM THE GROUP CONSISTING OF WOOD PITCH, GILSONITE, ROSIN, ASPHALT, COAL TAR PITCH AND PETROLEUM PITCH, HAVING A MELTING POINT IN THE RANGE OF 250* TO 350* F., COMBINED WITH 0.25 TO 1.5 PARTS (DRY WEIGHT) OF A SYNTHETIC RESIN SELECTED FROM THE GROUP CONSISTING OF PHENOL-FORMALDEHYDE, UREA-FORMALDEHYDE AND MELAMINE-FORMALDEHYDE RESINS, SAID RESIN BEING IN THE FORM OF AN AQUEOUS DISPERSION CONTAINING 50% TO 80% SOLIDS BY WEIGHT, AND AN AQUEOUS MENTRUUM CONSISTING OF 25% TO 75% WATER BY WEIGHT AND THE REMAINDER BEING A WATER-MISCIBLE ORGANIC SOLVENT HAVING A BOILING POINT IN THE RANGE OF 108* TO 325* F., THE QUANTITY OF SAID AQUEOUS MENSTRUUM BEING 75% TO 150% OF THE TOTAL WEIGHT OF THE SWELLING CLAY, RESINOUS ORGANIC BINDER AND SYNTHETIC RESIN. 